1. Field of the Invention
The present invention relates to a golf ball with a core and a cover surrounding the core. Particularly, the present invention relates to a thread-wound golf ball that exhibits great carry distance with favorable hit feeling, and that easily comes to a halt even though exhibiting high spinning when shot from the rough or when shot in a raining condition such as a balata covered golf ball.
2. Description of the Background Art
Conventional golf balls formed with a thread-wound layer around a liquid center and surrounded by a balata cover are widely used by low-handicapped golfers and professional golfers. However, the structure of such golf balls has the disadvantage that the fabrication process is difficult and the cut resistance is inferior. Various soft cover materials have been recently proposed as a substitute for balata covers.
For example, U.S. Pat. No. 4,884,814 discloses the usage of soft ionomer resins for the basic resin of the cover.
Also, the basic resin of a cover disclosed in GB2311530 is formed having as the main component a heated mixture of two components, i.e. ionomer resin, and a styrene-butadiene-styrene block copolymer including a polybutadiene block containing an epoxy group or a styrene-isoprene-styrene block copolymer including a polyisoprene block containing an epoxy group. This publication proposes a golf ball characterized in that the cover composition forming the cover has a flexural modulus of 50-300 MPa and a Shore D hardness of 40-60.
The inventors of the present invention have already proposed a golf ball directed to improve the hit feeling and the spin rate when shot with a short iron by virtue of the usage of a solid rubber center including oily substance and a soft cover material (U.S. Pat. No. 5,716,293).
However, the bounce and the hit feeling are not completely satisfactory since oil-resistant rubber or ionomer resin of high hardness is employed for the outer side of the solid rubber center. With the conventional soft cover material, the spin rate in a wet condition is inferior to the spin rate in a dry condition. Therefore, these golf balls were not satisfactory also from the aspect of spin maintenance.
An object of the present invention is to provide a thread-wound golf ball solved in the problems encountered in conventional thread-wound golf balls, exhibiting soft and favorable hit feeling with a great carry distance such as a thread-wound golf ball with a liquid core, and that can easily come to a halt though the spin rate is great when shot from the rough or when shot in a raining condition such as a balata-covered golf ball.
The above object is achieved by a golf ball of the present invention set forth in the following.
According to an aspect of the present invention, a thread-wound golf ball is constituted by a core, a rubber thread layer surrounding the core, and a cover formed of a mixture of ionomer resin, thermoplastic elastomer and a tackifier, having a Shore D hardness of at least 40 and not more than 65.
According to another aspect of the present invention, a thread-wound golf ball includes the above core, wherein the core is formed of two layers of an inner layer core having a diameter of 24-33 mm and the JIS-A hardness of at least 5 and not more than 50, and an outer layer core covering the inner layer core, having a thickness of 0.5-5 mm and a diameter of 25-35 mm with a Shore D hardness of at least 10 and not more than 60. The outer layer core is formed of thermoplastic resin and/or thermoplastic elastomer.
According to a further aspect of the present invention, the thermoplastic elastomer forming the above cover of a thread-wound golf ball includes a styrene-butadiene-styrene block copolymer (SBS structure), or a hydrogenate thereof, or a modified product thereof.
According to still another aspect of the present invention, the thermoplastic elastomer forming the above cover of a thread-wound golf ball includes a styrene-isoprene-styrene block copolymer (SIS structure), or a hydrogenate thereof, or a modified product thereof.
According to a still further aspect of the present invention, the above tackifier in a thread-wound golf ball includes terpene resin and/or rosin ester resin.
According to yet a further aspect of the present invention, the thermoplastic elastomer forming the outer layer core of a thread-wound golf ball includes a mixture of one or at least two types of polystyrene based elastomer, polyolefin based elastomer, polyurethane based elastomer, and polyester based elastomer.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawing.